1. Field of the Invention
The present invention is directed to a self-contained exothermic chemical heater which is heat recoverable and has a plurality of separate compartments to maintain the proper mixing and distribution of the chemical means disposed therein. More specifically, the present invention relates to a self-contained heat recoverable chemical heater employed with a heat recoverable sleeve or other member.
2. Description of the Prior Art
Heat recoverable polymeric articles are widely known and find many uses. Such articles typically recover from their heat unstable states by being exposed to open flames or heat guns. In some environments, the use of an open flame would be hazardous and an electrical power source might not be available.
It has been proposed to use a self-contained chemical heater with heat recoverable tubular articles. See, for example, Chapin, U.S. Pat. No. 3,924,603 and Wetmore, patent application Ser. No. 3,563. A self contained chemical heater has many known advantages and uses since no flame is produced, and no source of electricity is required. Consequently, many such devices are known in the art. However, many difficulties would be encountered if these devices are used with heat recoverable sleeves or the like. Heat applied to a heat recoverable sleeve surrounding a substrate therein must be evenly and steadily applied during the entire recovery period to promote uniform recovery in all parts of the sleeve and to form an effective bond.
The chemical heaters known in the art, such as Chapin, U.S. Pat. No. 3,924,603, Caillouette, U.S. Pat. No. 3,175,558, and Foster, U.S. Pat. No. 2,157,169 encounter serious deficiencies in this regard. Since these chemical heaters are not heat recoverable themselves, they would begin to lose contact with the enclosed heat recoverable sleeve as they generate heat and the sleeve recovers. As the recovery of the sleeve continues, the gap between the chemical heater and sleeve would widen, thereby decreasing the amount of effective heat which reaches the sleeve. This would not only interfere with the uniform recovery of the sleeve, but also create an additional problem when a heat activatable adhesive is employed with the heat recoverable sleeve. Oftentimes such an adhesive is used to form an effective environmental seal. Continuous application of the heat after recovery of the sleeve causes the adhesive to flow and form such a seal. However, without continuous thermal contact, insufficient heat would reach the sleeve and adhesive, thereby hindering the intended flow of the adhesive. Thus, the effectiveness of such a chemical heater would be limited whenever a heat activatable adhesive is employed with the heat recoverable sleeve.
A related problem encountered in the art concerns the method of mixing the chemical means to provide heat. Ideally, when used with heat recoverable sleeves the chemical means should mix rapidly in order to avoid a prolonged heat build-up time and to minimize possible hot spots. Moreover, the chemical means should be quickly distributed throughout the heater to avoid localizing the application of heat to portions of the sleeve, which would cause nonuniform recovery. Nor is it desirable that agitation of the chemical heater be required to promote the mixing and distribution of the chemical means since the high temperatures which are required with heat recoverable members would make the heater extremely difficult to handle manually. However, the chemical heaters known in the art usually divide the different chemical means into two separate containers. Normally, one of the containers is inserted into the other, and the chemical means are mixed by applying sufficient pressure to cause the inner container to rupture. This means of mixing the chemicals, however, initially produces heat only at the spot where the inner container ruptures. This is caused by the incomplete or inefficient mixing of the chemicals. Therefore, the heaters known in the art frequently must be agitated in order to mix and properly distribute the chemical means in order to effectively achieve the heat which would be required for the uniform recovery of a heat recoverable article. Consequently, the time and effort which is required to attain the proper uniform temperature is detrimental to their use.
Typically, the chemical heaters known in the art use a single, continuous container to hold each chemical means. A recurring problem with such heaters is that, commonly, the chemical means will migrate to one portion of the container and harden or "set-up." When the barrier between the container is ruptured, the heat produced is localized to the area where the chemicals can be mixed. Therefore, the heater cannot uniformly apply the heat it generates to the substrate.
These types of problems limit the usefulness of self-contained chemical heaters known to the art as a means to achieve recovery of heat recoverable sleeves or other such substrates.